Occurrence and D-Tryptophan Application for Controlling the Growth of Multidrug-Resistant Non-O157 Shiga Toxin-Producing <i>Escherichia coli</i> in Dairy Products

The objectives of the current study were first to determine the prevalence of non O157:H7E. coli, especially Shiga toxin-producing Escherichia coli (STEC) in retailed milk and dairy products in Egypt. Second, the antimicrobial resistance profiling and virulence genes of the isolated E. coli strains were screened. Third, evaluation of the inhibitory effects of D-tryptophan against E. coli O26:H11 was further performed. The results revealed that 20% (30/150) of the samples were STEC positive, with 64 isolates harboring some virulent genes, such as Stx1, Stx2, eaeA, and hylA. Serological identification revealed four different pathotypes belonging to EPEC, ETEC, EHEC, and EIEC. Antimicrobial susceptibility testing revealed that 100%, 98.44%, 92.19%, 71.87%, 65.63% and 64.06% of the isolates had a resistance against tetracycline, oxacillin, erythromycin, nalidixic acid, sulphamethoxazol, and ampicillin, respectively. D-tryptophan addition (40 mM) to E. coli O26:H11-inoculated soft cheese and ice cream revealed a significant reduction (p < 0.05) in bacterial growth, especially when accompanied with other food stressors. D-Tryptophan is considered as an effective food preservative and as a promising alternative candidate in the dairy industry

Heavy metal residues in milk and some dairy products with insight into their health risk assessment and the role of Lactobacillus rhamnosus in reducing the lead and cadmium load in cheese

Heavy metals were analyzed in buffalo's milk and some dairy products assembled from different dairy farms, supermarkets, and vendors in Mansoura, Egypt. The mean concentrations (mg/kg wet weight) of the heavy metals detected in raw milk, Kareish cheese, processed cheese, and milk powder were 0.0014, 0.0378, 0.0022, and 0.0204, respectively for mercury; 0.012, 0.0764, 0.052, and 0.120, respectively for arsenic; 0.1016, 0.2924, 0.1256, and 0.3352, respectively for lead; 0.07, 0.1172, 0.0576, and 0.1252, respectively for cadmium; 0.1044, 0.174, 0.1016, and 0.208, respectively for chromium; and 0.0656, 0.188, 0.1272, and 0.2496, respectively for copper. The probiotic Lactobacillus rhamnosus was incorporated into soft cheese as an attempt for reducing lead and cadmium whose concentrations were diminished by 81.5% and 74.5%, respectively within 48 h at 4 °C. The study concluded that although the maximum limit of Pb and Cd has been exceeded in 44% to 68% of the dairy products tested, the health risk assessment indices comprising Estimated Daily Intakes, Provisional Tolerable Daily Intakes, Target Hazard Quotient, and Hazard Index indicated no potential health risk upon consumption of such dairy products analyzed. The study also suggested the use of Lactobacillus rhamnosus probiotic for minimizing lead and cadmium levels in dairy food